E-ZPass and other electronic toll collection systems are emerging as a powerful means of proving infidelity. That's because when your spouse doesn't know where you've been, E-ZPass does.

"E-ZPass is an E-ZPass to go directly to divorce court, because it's an easy way to show you took the off-ramp to adultery," said Jacalyn Barnett, a New York divorce lawyer who has used E-ZPass records a few times.

Lynne Gold-Bikin, a Pennsylvania divorce lawyer, said E-ZPass helped prove a client's husband was being unfaithful: "He claimed he was in a business meeting in Pennsylvania. And I had records to show he went to New Jersey that night."

Of the 12 states in the Northeast and Midwest that are part of the E-ZPass system, agencies in seven states provide electronic toll information in response to court orders in criminal and civil cases, including divorces, according to an Associated Press survey.

In four of the 12 states, including New Jersey and Pennsylvania, highway authorities release E-ZPass records only in criminal cases. West Virginia parkways authority has no policy. (Divorce attorneys in some cases can still obtain toll records from the other spouse rather than a highway agency.)

The Illinois Tollway, which hands over toll records, received more than 30 such subpoenas the first half of this year, with about half coming from civil cases, including divorces, according to Joelle McGinnis, an agency spokeswoman.

The New Jersey Turnpike Authority said it turns down about 30 subpoenas in civil cases every year, about half of them divorces.

Electronic toll records have also proved useful in criminal cases.

They played a role in the murder case against Melanie McGuire, a New Jersey nurse convicted in April of killing her husband and tossing his cut-up remains into the Chesapeake Bay in three matching suitcases in 2004. Prosecutors used toll records to reconstruct her movements.

Davy Levy, a Chicago divorce lawyer for more than 30 years, said toll records from I-Pass (part of the E-ZPass system) are useful in catching a spouse in a lie.

"You bring up the I-Pass records and it destroys credibility," said Levy, who has used such records two or three times for such purposes.

The E-ZPass network covers about half the East Coast and part of the Midwest, with about 2 billion charges per year. That can mean a lot of records. One of the busiest toll plazas in New Jersey, the Garden State Parkway's southbound Raritan plaza, gets about 90,000 E-ZPass hits per day.

Some worry that using those records for other purposes is a violation of drivers' privacy.

"When you're marketed for this new convenience, you may not realize there are these types of costs," said Nicole Ozer of the American Civil Liberties Union of Northern California.

Bob Barr, a former Republican congressman from Georgia turned Libertarian and privacy rights advocate, said people who want to protect their privacy shouldn't use electronic toll systems.

"People are foolish to buy into these systems without thinking, just because they want to save 20 seconds of time going through a toll booth," he said.